In distributing the video or sound as digital data (digital contents), it is common practice to embed the electronic watermark information (digital watermark) in the digital contents in order to designate a source of the digital contents or enhance the security.
Nowadays, various kinds of digital contents are distributed on-line via a network such as the Internet, in which there is a demand for an application for adding the information (identification information) different for each distribution destination or user in distributing the digital contents, as prevention means for preventing illegal use of the distributed digital contents, and means for designating a secondary distribution destination (this application is hereinafter referred to as a fingerprint). To implement this fingerprint, the additional information may be described in a format header of the digital contents. However, considering that the distributed digital contents are possibly subjected to various edits including compression, DA/AD conversion, and format conversion, it is effective to embed the additional information to the digital contents themselves, employing a digital watermark technique.
As above described, one problem is that in the fingerprint, it is required to change the information added to the digital contents for each user to access or each distribution destination. However, a process of embedding the digital watermark to the digital contents comprises calculating an operation amount in a range without influence on the quality of digital contents themselves (without deterioration in the visual or aural elements), whereby the processing calculation cost is generally very high. Therefore, if a different digital watermark is embedded for each access to the digital contents, a server providing the digital contents (hereinafter referred to as a contents server) has a very high load.
In a digital contents distributing system practically on-line, it is required for a plurality of users to gain access simultaneously and acquire desired digital contents. However, in the above system where the contents server has high load, the number of users capable of gaining access simultaneously can not be increased to lack the practicality of the system.
In the case where the digital contents are distributed in the recent network system, the digital contents of distribution object are usually non-reversibly compressed due to a limited bandwidth in the network environment. Therefore, it is required to perform a process of unpacking and recompressing the digital contents to embed a digital watermark, so that the contents server has more load.
Particularly, in a streaming distribution in which the contents distribution in real time needs to be guaranteed for each user, it is a significant problem that the contents server has an increased load.